[fix] name mapping in request data classes

[joelbutcher]

This PR adds a snake case name mapper PHP attribute to BaseData.

closes #225

Problem Context

As discovered in #225, the API tests are returning a false positive, because of the Laravel Data configuration used for testbench:

    'name_mapping_strategy' => [
        'input' => \Spatie\LaravelData\Mappers\SnakeCaseMapper::class,
        'output' => \Spatie\LaravelData\Mappers\SnakeCaseMapper::class,
    ],

Setting both of these values to NULL and running the test suite highlights the error. Of course, this is fine in our tests as we are specifying the Laravel app to uses these mappers. However applications consuming this package might not have Laravel Data configured this way.

The fix

Since we have architectural tests in place to ensure that all XyzRequestData classes must be declared final and must extend BaseData, we are able to fix the problem by simply adding the following attribute above the class declaration for BaseData:

#[MapName(SnakeCaseMapper::class)]
abstract class BaseData extends Data
{
   ...
}

[sconnole]

thanks for the fix @joelbutcher 👍